It is known that a tuning fork coupled to a suitable drive circuit will resonate at a frequency that is a function of the tuning fork temperature. An oscillator comprising the tuning fork and drive circuit can therefore be used to measure the temperature of the environment in which the tuning fork is located. In one well-known tuning fork temperature sensor, the tuning fork base is secured to a supporting structure, and a tuning fork tines vibrate torsionally or flexurally about their longitudinal axis. Examples may be found in U.S. Pat. Nos. 4,437,773 and 4,472,655. As the temperature of the tuning fork varies, the frequency of oscillation varies over a predetermined operating range. This behavior differs from tuning fork frequency standards that are designed specifically to be insensitive to temperature and operate at a single frequency.
Although a sensor based on a tuning fork oscillator is capable of providing very accurate temperature measurements, there are a number of problems with such sensors that to date have limited their usefulness. In particular, tuning fork temperature sensors often exhibit significant and generally unpredictable nonlinearities and discontinuities at particular temperatures or frequencies within their intended operating ranges. Such nonlinearities and discontinuities are commonly referred to as activity dips. In the past, the cause of activity dips has remained speculative, and no effective techniques have been provided for their elimination. As a result, each tuning fork to be used in a temperature sensor had to be individually checked to determine whether any activity dips occurred within the intended operating range. If such activity dips did occur, the tuning fork was discarded. Such screening procedures are extremely inefficient and costly, and the need to use such procedures has significantly inhibited the application of tuning fork temperature sensor techniques. This problem does not occur in frequency standard tuning fork oscillators which only operate at a single frequency.